Thomas Newman’s imaginative soundtrack brings to life the aquatic world of Pixar’s latest adventure. “Kelpcake” catches the twinkle of sunlight through the ocean surface, as well as an undertow’s strong but unseen current. True to its title, “Open Ocean” is full of floating textures that shift from sharp and rapid to ethereal over the course of the arrangement. Tension builds on “One Year Later,” but Newman always returns to passages of reflection. Jon Brion’s woozy themes are a touchstone for “Unforgettable,” in which Sia’s elegant voice dances with a undulating string arrangement—an ingenious reinvention of a familiar favorite.